This invention relates to an optical pickup for use in an optical apparatus such as an optical disk drive and, more particularly, to an optical pickup capable of preventing an inclination of an optical axis of an objective lens upon focusing an optical beam on an optical disk.
Referring to FIGS. 1 and 2, a conventional optical pickup 1 comprises a damper base 2, two pairs of suspension wires 3 and 4 (in the figures, one suspension wire alone is illustrated in each pair) having one ends fixed to the damper base 2, a lens holder 5 attached to the other ends of the suspension wires 3 and 4 and elastically supported by the suspension wires 3 and 4 to be swingable and returnable to a predetermined position, an objective lens 6 held by the lens holder 5, a focusing coil 7 attached to the lens holder 5, a first magnetic circuit 8 intersecting one side of the focusing coil 7 which is faced to the damper base 2, and a second magnetic circuit 9 intersecting the other side of the focusing coil 7 which is opposite to the one side.
In the conventional optical pickup 1, the first magnetic circuit 8 has a magnetic flux density equal to that of the second magnetic circuit 9. Therefore, a first force F1 produced between the first magnetic circuit 8 and the focusing coil 7 has an intensity equal to a second force F2 produced between the second magnetic circuit 9 and the focusing coil 7.
The optical pickup 1 further comprises a tracking coil, an optical base, a laser diode, a polarization beam splitter, a collimator lens, a reflection mirror, and a photo diode, although not shown in the figure. These components are irrelevant to the gist of this invention and will not be described herein.
The conventional optical pickup 1 is designed so that an optical axis O of the objective lens 6 is kept in parallel to the vertical direction when the lens holder 5 is moved in a focusing direction (tangential direction) FC of the objective lens 6. In practical use, however, due to various factors known in the art, movement of the lens holder 5 in the focusing direction FC of the objective lens 6 causes predetermined tilting variation of the optical axis O of the objective lens 6 in either a first mode or a second mode which will presently be described.
In the first mode, when the lens holder 5 is shifted upward from the predetermined position, the optical axis O, particularly, an upper portion thereof is inclined towards the damper base 2 as shown in FIG. 2A. When the lens holder 5 is shifted downward from the predetermined position, the upper portion of the optical axis O is inclined away from the damper base 2 as shown in FIG. 2B.
In the second mode, when the lens holder 5 is shifted upward from the predetermined position, the upper portion of the optical axis O is inclined away from the damper base 2 as shown in FIG. 3A. When the lens holder 5 is shifted downward from the predetermined position, the upper portion of the optical axis O is inclined towards the damper base 2 as shown in FIG. 3B.
Upon occurrence of the tilting variation of the optical axis of the objective lens, the optical pickup is deteriorated in characteristics.
It is therefore an object of this invention to provide an optical pickup which is capable of preventing tilting variation of an optical axis of an objective lens during movement of a lens holder in a focusing direction of the objective lens to thereby prevent deterioration in characteristics of the optical pickup.
Other objects of the present invention will become clear as the description proceeds.
According to the present invention, there is provided an optical pickup which comprises a damper base, a lens holder having a first part and a second part which are spaced from each other in a predetermined direction, a suspension member elastically coupling the lens holder to the damper base to make the lens holder be movable relative to the damper base in a focusing direction perpendicular to the predetermined direction, an objective lens held by the lens holder, a focusing coil fixed to the lens holder, a first magnetic circuit connected to the damper base and coupled to the focusing coil for generating first force in cooperation with the focusing coil to urge the first part of the lens holder in the focusing direction, the first magnetic circuit having a first magnetic flux density, and a second magnetic circuit connected to the damper base and coupled to the focusing coil for generating second force in cooperation with the focusing coil to urge the second part of the lens holder in the focusing direction, the second magnetic circuit having a second magnetic flux density different from the first magnetic flux density.